The present invention relates to the field of color monitors or video screens, and, more particularly, to color monitors for computers.
Each visible image on a color monitor includes three color cues, namely red, green and blue. In the case of a color monitor for a computer, these three color cues originate from the computer and are sent to a pre-amplifier to be set and controlled. The color cues are then sent to an amplifier and are finally directed to the three cathodes of the cathode-ray tube of the monitor. The pre-amplifier and the amplifier are generally arranged in the same framework as the cathode-ray tube.
The final factory calibration of the monitor includes two fundamental adjustments. The first is the black adjustment (also referred to as the xe2x80x9ccut-offxe2x80x9d adjustment). This adjustment involves setting, for each pathway (i.e., for each color) the voltage required at the output of the amplifier or of the pre-amplifier to have a black color image. The second adjustment is the white adjustment (also referred to as the xe2x80x9cdrivexe2x80x9d adjustment) which involves adjusting, for each pathway, the voltage required at the output of the pre-amplifier to have a white color image. A nominal white to be displayed on the screen includes a defined proportion of the three base colors (i.e., red, green and blue) and is measured by an appropriate apparatus, such as a color camera placed in front of the monitor.
The behavior of the cathode-ray tube is not identical for the three pathways, and the above two adjustments are aimed at compensating for the differences in the tube from one pathway to another. Moreover, the behavior of a given pathway varies from one tube to another, which requires individual adjustment upon leaving the manufacturing line.
The user of the monitor benefits from a so-called xe2x80x9cbrightnessxe2x80x9d adjustment, which enables him to set the luminosity level of the screen as a function of the ambient lighting or of the content of the image to be displayed. The brightness adjustment is made either using a thumbwheel placed on the framework of the monitor or by clicking on a brightness adjustment menu with the computer""s mouse, for example.
Presently, two amplifier and pre-amplifier architectures are known. The first, which is simple and economical, includes placing a brightness adjustment in the pre-amplifier after the white adjustment. The voltage corresponding to the brightness cue, which is the same for the three pathways, is not affected by the white adjustment. It follows that the proportionality between the three pathways which is set by the white adjustment and is effected for a nominal value of the brightness adjustment will not be preserved if the brightness adjustment is modified by the user. This results in a modification of the characteristics of the white color when the brightness is set by the user. This architecture exhibits a factory adjustment procedure which is easy to implement since the two adjustments (i.e., black and white) are independent. The quality of the image is not, however, entirely satisfactory.
The second known architecture includes placing a brightness adjustment in the pre-amplifier ahead of the white adjustment. Thus, the voltage corresponding to the brightness cue is modified by the white adjustment and the proportionality between the three pathways is maintained irrespective of the value of the brightness adjustment. This results in better visual comfort for the user since-the original white color established for a nominal brightness signal will always be preserved.
Unfortunately, this architecture has the drawback of being difficult to implement during factory adjustment since the initial adjustment of the black is modified by the adjustment of the white. Consequently, the adjustment of the black must be repeated once the adjustment of the white has been made and so on. Definitive adjustment is achieved after several iterations, this resulting in a non-negligible time loss during fine-tuning in the factory. This time loss is typically on the order of about ten seconds. This results in an increase in manufacturing costs and increased complexity of the manufacturing line.
An object of the present invention is to provide a process and a device for color adjustment of a color monitor which is economical, simple, and can yield a high quality image.
This and other objects, features, and advantages according to the invention are provided by a process for the color adjustment of a color monitor including a cathode-ray tube and a circuit or means for adjusting the brightness. The process includes providing a nominal brightness signal downstream of a circuit or means for adjusting the white level and upstream of a circuit or means for adjusting the black level. Furthermore, a voltage required to obtain a black color image is set and the voltage required to obtain a white color image is set. The nominal brightness signal may be provided upstream of the means for adjusting the white level. Also, the voltage required to obtain a black color image is set.
Preferably, the cathode-ray tube is provided with a plurality of pathways, and the settings are effected for each of the pathways. The voltage setting required to obtain a black color image may be made at an output of an amplifier included in the monitor. Additionally, the voltage setting required to obtain a black color image may be made at an output of a pre-amplifier included in the monitor. Further, the voltage setting required to obtain a white color image may be made at the output of the pre-amplifier. The color of the image is also preferably measured.
A device according to the present invention for color adjustment of a color monitor including a cathode-ray tube includes means for adjusting the brightness, a means for setting the voltage required to obtain a black color image, and a means for setting the voltage required to obtain a white color image. The device may further include means for adjusting the brightness upstream of the means for setting the voltage required to obtain a white color image and means for adjusting the brightness downstream of the means for setting the voltage required to obtain a white color image.
Advantageously, the device may include a single means for adjusting the brightness that is able to be active alternately upstream and downstream of the means for setting the voltage required to obtain a white color image. The device may also include switching means at an output of the means for adjusting the brightness for connecting the output of the means for adjusting the brightness alternately to an input and to an output of the means for setting the voltage required to obtain a white color image. A monitor is also provided according to another embodiment of the present invention comprising an adjustment device such as that described above.
According to the invention, the steps for calibrating a color monitor at the end of the production line have a duration of around 1 to 2 seconds, as compared to the duration of adjustment required for the first architecture of the prior art noted above. Furthermore, this is done while preserving the initial adjustment of the white color, irrespective of the brightness selected by a user of the monitor.
The present invention therefore makes it possible to obtain the advantages of each of the prior art architectures without suffering from their respective drawbacks. Moreover, the video amplification architecture in accordance with the invention remains relatively simple in that it adds a switching means which is common for the three pathways. The adjustment device according to the invention is therefore simple and relatively economical.